Insulin mediated glucose uptake occurs largely in skeletal muscle via insulin's action to increase cellular membrane permeability to glucose. In addition, skeletal muscle perfusion can modulate the rate of insulin mediated glucose uptake. Physiologic insulin concentrations cause an approximately 2 fold increase in skeletal muscle blood flow. Thus, enhanced muscle perfusion may be integral to insulin's overall action to promote insulin mediated glucose uptake and conversely, impairment of this hemodynamic effect could contribute to insulin resistance. Insulin mediated vasodilation is impaired in insulin resistant states such as obesity, non-insulin dependent diabetes and essential hypertension. Based on recent data indicating that insulin vasodilates by modulating the release of endothelium derived Nitric Oxide (EDNO) and that insulin resistant subjects exhibit impaired vasodilation we propose to test the overall hypothesis that insulin modulation of the EDNO system is impaired in states of insulin resistance. To this end we plan:1) To assess insulin mediated EDNO dependent skeletal muscle vasodilation over a range of insulin sensitivity. Intrafemoral artery infusions of L-NMMA (an inhibitor of EDNO synthesis) , methacholine (which releases EDNO) and sodium nitroprusside (an exogenous nitric oxide) will be performed at baseline and during euglycemic hyperinsulinemic clamp studies. 2)To evaluate the effect of hyperglycemia on endothelium dependent vasodilation. Given that hyperglycemia superimposed upon insulinemia causes vasodilation we will test whether i) glucose induced vasodilation is EDNO dependent and ii) that the rate of glucose metabolism is the major determinant of EDNO dependent vasodilation. 3)To determine the contribution of insulin mediated skeletal muscle vasodilation to insulin action. i)insulin sensitivity, responsiveness and the time course of insulin stimulated leg muscle glucose uptake will be measured during intrafemoral artery infusions of L-NMMA designed to blunt the normal rise in muscle perfusion, and ii)rates of leg glucose uptake will be measured during infusions of substances designed to increase (normalize) leg blood flow in insulin resistant subjects; 4)To quantitate rates of In Vivo EDNO turnover 15N-L-arginine (a precursor of EDNO) will be given intravenously to estimate basal and insulin stimulated whole body EDNO production rates and orally to estimate splanchnic EDNO production rates; S) To define the mechanism of perfusion modulated glucose uptake by Positron Emission Tomography (PET). Thigh muscle perfusion (0-15- water) and glucose uptake (FDG) will be measured by PET. Tracer injections will be performed at baseline, and during euglycemic hyperinsulinemic clamps to quantitate the effect of insulin on skeletal muscle specific blood flow and FDG utilization. Given that EDNO decreases vascular tone, reduces platelet aggregation and thrombosis and inhibits mitogenesis, a defect in insulin's ability to modulate EDNO could contribute to the increased risk of-atherosclerosis in insulin resistant states .This proposal will provide new insights into the in vivo regulation of the EDNO system by insulin, glucose and insulin resistance.